Faces are often easier to hide than the emotions.
Masks are very popular among Vietnamese females of all ages. The reason for this is very interesting. Apparently, Vietnamese males love fairer complexions. It is considered more attractive and beautiful. So, the females try to save their faces from the scorching sun in the daytime by wearing masks (and hats sometimes). Not all males are happy about this practice though. Because, sometimes they can't recognize their friends and acquaintances even from a close distance.
Here the face is hidden, but the smile isn't.